It is conventional to use a meter having a deflectable needle to indicate audio signal amplitude. In such a meter, the needle deflection is normally directly proportional to signal amplitude, but the meter scale is usually calibrated in decibels because the perception of loudness is a logarithmic function of signal amplitude. An analog audio meter of this type suffers from the problem that its useful dynamic range is very small compared to the dynamic range of audio signals. The amplitude of a signal that is 20 dB below full scale is one-tenth of full scale amplitude, but audio program material typically has a dynamic range exceeding 60 dB. Consequently, most of that range will barely deflect a linear meter.
Many methods are used to make the indication given by a conventional analog meter more logarithmic, or dB-linear, in order to increase the dynamic range over which the needle is deflected to a readily-perceptible degree, including use of nonlinear meter movements and log-shaping networks.
Electronic bar graph meters employ multiple light-emitting diodes (LEDs). It is conventional to use such bar graph meters to indicate audio signal amplitude, and log-weighted amplitude sensing circuits are used in order to provide a dB-linear display.